1. Field of the Invention
The invention relates to an arrangement for the suspension of wheels in a working machine movable on a terrain.
2. Description of the Related Art
For harvesting, working machines are known which move on a terrain by means of wheels, including harvesters in which a harvesting device is provided at the end of a boom assembly, a so-called harvester head for cutting and felling a tree stem and sawing it to pieces of desired length. The sawn tree stems are collected by a loading apparatus, i.e. a forwarder equipped with a grapple, and transported in the load space.
Publication WO 89/00928 discloses a working machine which comprises two frames connected to each other by means of a joint. The joint is used to control the direction of motion, wherein the working machine is provided with articulated steering. A swivel base is mounted on the frame to swivel around a vertical axis and is equipped with a cabin and, by its side, a boom assembly, a harvester head being mounted at the end of the boom assembly. In a known manner, the boom assembly can also be mounted in front of the cabin or on a swivel base separate from the cabin. In forwarders of prior art, one of the frames is equipped with a load space where the tree stems are collected from the ground by means of a grapple mounted on the frame. The other frame is equipped with a cabin and a power source for the working machine. So-called combined machines are also known, combining the functions of a harvester and a forwarder. In this case, for example, the rear frame in the harvester is equipped with a load space. The advantage is that the harvesting and the collection of the tree stems can be performed simultaneously, wherein the need for several machines in the forest is reduced, which also reduces damage caused to growing stock.
For example in forest thinning, several growing trees are left by the side of the logging road used by the working machine, which limits the space available for the working machine, particularly in the width direction. In the working machine according to the WO publication, the suspension of wheels is implemented with a joint parallelogram comprising articulated, parallel upper and lower suspension arms. A cylinder for controlling the position of the wheel is coupled between the joint of the upper suspension arm on the frame side and the joint of the lower suspension arm on the wheel side. The joint parallelogram also keeps the wheel vertical in different positions.
The suspension of wheels according to prior art is problematic particularly when there is a need to limit the dimensions of the working machine, particularly its width and height, without affecting the other properties, particularly the capability to proceed on the terrain. The problem is that the cylinder is mounted at a point where the piston stroke of the cylinder becomes very long for moving the wheel from the upper position to the lower position. For this reason, the arms also become long, to fit the cylinder in between, both short and long, which affects particularly the width of the working machine, and it is particularly difficult to make the long suspension arms steadfast.
Another problem is that when there is a need to reduce the width of the working machine, the moment arm of the cylinder must be made shorter, wherein said suspension arms must be made shorter. The moment arm is formed by the transverse distance between the cylinder and the joint of the lower suspension arm on the frame side. Reducing the length of the suspension arms will also cause that the play between the upper position and the lower position is reduced. In particular, the moment arm is reduced when the joints of the lower and upper suspension arms on the frame side are brought closer to each other to limit the height of the frame. The reduction of the length of the tension arm increases the power required of the cylinder, leading to a larger cylinder and/or a higher pressure level, which is not always preferred. Consequently, a modification of the presented wheel suspension, particularly a modification of the length of and distance between the suspension arms, will strongly affect the moment arm, wherein it is difficult to modify the structure, particularly the mountings.
It is an aim of the present invention to eliminate the above-presented problems by means of a wheel suspension without increasing the width of the working machine, decreasing the steerability and complicating the constructions.
The main principle in the invention is that the corresponding joints of the joint parallelograms of the wheels placed on different sides of the frame, on the frame side, are placed on the same axis of rotation. In other words, the joints of the upper suspension arms are placed on the same axis of rotation and/or the joints of the lower suspension arms are placed on the same axis of rotation. The rotation axes are preferably placed on the centre line of the working machine. Thus, the width of the working machine can be reduced, particularly at the location of the wheels, without reducing the length of the moment arms and in comparison with the prior art. Without affecting the width, the working machine can also be equipped with wider tyres, or the wheels can be equipped with large turning cylinders for steering the wheels.
Another central principle of the invention is that the width of the machine can be further reduced in such a way that at least some of the joints on the frame side, preferably the joints of the suspension arms pairwise, are placed on the other side of the central line, opposite to the wheels. The suspension arms are thus placed diagonally with respect to each other and seen from the direction of the rotation axis. The joints of the other suspension arms can thus be located on the central line or closer to the wheel. With this arrangement and the same machine width, it is possible to achieve a longer adjustment of the wheels in the height direction or a smaller dish of the wheels. In prior art, the joints and the wheels are located on the same side of the centre line.
By placing the cylinder in a vertical position and mounting its one end to the lower suspension arm and its other end to the frame, it is possible to reduce the piston stroke of the cylinder when compared with prior art. However, the moment arm of the cylinder can be kept substantially the same as in prior art, but the mounting point in the lower arm can be shifted closer to the frame. Thus, there will be more space for other structures at the outermost end of the suspension arms. Thanks to the shorter piston stroke, the vertical cylinder does not harmfully increase the height of the structure. As the mounting point is placed in the suspension arm and not in its joint, a change in the length of the suspension arm will not necessarily affect the structure of the cylinder, the pressure levels used, or particularly the moment arm. With the vertical position, also the moment arm formed by the suspension arms in different positions will be less changed when the wheel moves up and down.
It is also an aim of the invention to provide a compact module structure for the wheel suspension and the frame structure in various working machines.
In the following, the invention will be described in more detail by using as an example an advantageous embodiment of the invention with reference to the appended drawings, in which